This invention relates to a semiconductor device having a diode structure of FRD (Fast Recovery Diode) type, and more particularly to a fast semiconductor device having a lateral diode structure and improved switching characteristics (or recovery characteristics).
Some semiconductor integrated circuit devices for in-vehicle and small motor control applications require relatively high withstand voltage and fast switching rate. A typical diode provided in the semiconductor integrated circuit device meeting such requirements, called “lateral diode”, has a structure including a p-type substrate on which an n+-type buried layer and an n+-type diffusion layer are formed and isolated from the substrate potential (e.g., Japanese Laid-Open Patent Application 2003-92414). In this example, a RESURF (REduced SURface Field) layer is provided at the edge of the cathode to alleviate the electric field and maintain the withstand voltage of the diode at a high level.
On the other hand, faster switching rate is also increasingly required. However, previous attempts to provide a lateral diode of a faster rate involve the following problems.
In a lateral diode having a junction of a p−-layer and an n−-layer, minority carriers (i.e., holes) have been accumulated in the n−-layer when a bias voltage is about to be turned off from forward to reverse. Sweeping out the accumulated carriers from the anode electrode of the diode at the time of turn-off will deteriorate the switching characteristics (e.g., turn-off time) because current flows from the n—layer to the anode electrode until the carriers are completely swept out.